Sound reproducing apparatus



Nov. 24, 1931. L. v. F'OESTER SOUND REPRODUCING APPARATUS Filed Aug. 6. 1929 ER INVENTOR ATTORNEY I ducing sounds which have been lll BAUSOE & LOHIB OPTICAL "H NEW YORK, A. CORPORATION 01' m You com mnonmmro Arman-ca Application nea'anzm a, 1m. lerial It. scam.

This invention relates to the art of reprophoto phicelly recorded on film. In one met d of reproducin I sound from a photographic record, a suite is light source illuminates a very narrow slit and the image of this illuminated slit is rejected onto the sound record on the film. garying densities or areas of the sound record on the moving cause varying amounts of light to fell upon a light-sensitive cell so that current variations are set us in the circuit, of which the cell is a part, an by suitable apparatus are translated into sound, all as is well known in the art.

In reproducing sound in this manner, it is essential, for-the true and accurate production of sound, that a very sharp, bright, narrow image of the illuminated slit be projected onto the sound record on the film. In the prior practice, the ima of a straight linear slit has been projec onto the soun record. Due to the curvature of field introduced by the lens system, however, the projected time c which falls on the sound record is relative y sharp and clear at its middle portion but is indistinct and fuzzy at the two end portions. This causes a loss of tone quality and poor sound reproduction.

One of the objects of the resent invention is to provide an improve means for reproducing sound from a photographic sound record. Another object is to rovide sound reproducing menus which em odies an improved slit unit whereby a uniformly sharp,

clesr image of the illuminated slit will be projected onto the sound record on the film. 'lhese and other objects and advantages reside in certain novel features of construction, arrangement and combination of parts as will hereinafter be more fully explained and pointed out in the append claims.

Referring to the drawings:

Fig. 1 is a diagrammatic view showin a side elevation of e. system emying my 1nvention.

Fig. 2 is a diagrammatic view showing a top plan view of the s stem @ne embodiment o my invention is illustrsted in the drawings wherein a suitable light source 10, such as an incandescent ribbon filament, is ima ed b the cond lens unit 11 in mi1prov ed slit, indicazd generally at 12. y means of the objective lens system 13, a reduced ima e of the illuminated slit is projected onto the sound record track on the film 14. As the film 14 is moved, t e opaque and transparent portions of the sound record produce a variation in the intensity of lig t that passes through to the electrode 15 of the light-sensitive cell 16. These variations, in intensity, of the light falling on the electrode of the light-sensit1ve cell, produce corres onding vanati'ons in an electrical circuit w hich are amplified and translated into sound by methods well known to those skilled in the art.

My improved slit unit, indicated generally atl2, comprises two spaced opaque members 17 and 17' which are curved as shown in Fig. 2 with the concave side of the slitfacing the objective lens 13. Although the slit is shown on the drawings in exaggerated size for sake of clearness, in one embodiment which has been reduced to practice, the two members 17 and 17" are spaced 0.0015 inch apart'and the curvature of the slit is defined b an arc of a circle whose radius is 6.66 m" eters. It is to be understood, of course, that the slit may be made in other dimensions and formed of an suitable material by any desired meth-, od. us, for example, the slit could be made by depositing an opaque layer, such as copper or silver, on the surface of a less cylinder and then making a fine scratch or in the opaque layer to provide a narrow slit. The ruling would, of course, be made around the circumference of the cylinder in a plane perpendicular to the axis of the cylinder.

As hereinbe'fore stated, the reproducing systems of the prior art use a straight linear slit with the result that the tone quality is poor and the reproduction generally inferior. This is due to the fact that the projecting lens system introduces curvature of field so that the slit image which is projected onto the fiat film surface is relatively sharp and distinct at its central portion but is flared out and becomes indistinct and blurred at the end portions. When an image of this type is projected onto the'sound record on 1 2' Leeann the film, the flared out portions at the ends of the image cover several small elemental 11 its of the sound record, whereas the sharp, uniform, central portion ofthe ima e covers only one elemental unit of the soun record. Hence, such an image will cause the simultaneous reproduction of sounds from difierent elemental units of sound record, with the result that the tone quality and reproduction will not be true and accurate. If an attempt is made to correct the lens 13 for curvature of field, the working aperture of the lens is tly reduced so as to impair the success and eflicient operation of the reproducing 15 system- By means of my improved slit unit, however, I am able to project, onto the sound track on the film, an image of the slit which will be uniformly clear, sharp and distinct throughout its entire length, while still retaining the maximum working aperture of the o tical system, so that superior sound re ro uction and tone quality are obtained.

, arious modifications can obviously be u made without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

. 1. Apparatus for reproducing sound comprising a light source, a li ht-sensitive cell,

means defining an arcuate s 't positioned between said source and said cell with the convex side of said slit facing said source and a film positioned between said slit and said as cell, said film bearing a sound record.

2. Apparatus for re roducing sound from a hotographic soun record, comprising a lig 't source, opaque means defining an arcuate slit a condenser for imagin said source 40 in said slit, a light-sensitive ce and a lens system for projecting an image of said slit onto the sound record which is positioned between said system and said cell.

1 3. Apparatus for reproducing sound comprisin in combination means defining a curve slit,-a li ht source for illuminat' said slit with t e convex side of said slit facing said source, a lens system for projecting an image of said slit onto the sound 5 record on a film and a light-sensitive cell in position to receive light rays which pass through a sound record. i

pparatus for reproducing sound comprising spaced, opaque, arcuately curved members defining a curvedsslit, a light source for illuminating said slit, a light-sensitive cell, a sound record positioned. between said 'slitand said cell and lens means for pro ect1n an image of said slit onto said sound so recor the concave side of said slit being faced towards said lens means.

LEON V. FOSTER. 

